Variable Interest Entities	12 Months Ended
Dec. 31, 2017
Variable Interest Entities [Abstract]
Variable Interest Entities	11. Variable Interest Entities From time to time the Company may form joint ventures with third parties for the execution of single contracts or projects. In accordance with ASC 810, the Company assesses its joint ventures at inception to determine if any meet the qualifications of a VIE. The Company considers a joint venture a VIE if either (a) the total equity investment is not sufficient to permit the entity to finance its activities without additional subordinated financial support, (b) characteristics of a controlling financial interest are missing (either the ability to make decisions through voting or other rights, the obligation to absorb the expected losses of the entity or the right to receive the expected residual returns of the entity), or (c) the voting rights of the equity holders are not proportional to their obligations to absorb the expected losses of the entity and/or their rights to receive the expected residual returns of the entity, and substantially all of the entity’s activities either involve or are conducted on behalf of an investor that has disproportionately few voting rights. Upon the occurrence of certain events outlined in ASC 810, the company reassesses its initial determination of whether the joint venture is a VIE. ASC 810 also requires the Company to determine whether it is the primary beneficiary of the VIE. The Company concludes that it is the primary beneficiary and consolidates the VIE if the Company has both (a) the power to direct the economically significant activities of the VIE and (b) the obligation to absorb losses of, or the right to receive benefits from, the VIE that could potentially be significant to the VIE. The Company considers the contractual agreements that define the ownership structure, distribution of profits and losses, risks, responsibilities, indebtedness, voting rights and board representation of the respective parties in determining if the Company is the primary beneficiary. The Company also considers all parties that have direct or implicit variable interests when determining whether it is the primary beneficiary. In accordance with ASC 810, management’s assessment of whether the Company is the primary beneficiary of a VIE is performed continuously. As of December 31, 2017, the Company’s Consolidated Balance Sheet included current and noncurrent assets of $95.5 million and $11.6 million, respectively, as well as current liabilities of $140.7 million related to the operations of its consolidated VIEs. One large joint venture that the Company is consolidating was established to construct the Purple Line Segment 2 Extension project, a $1.4 billion mass-transit project in Los Angeles, California. The Company has a 75% interest in the joint venture with the remaining 25% held by O&G Industries, Inc. The joint venture was initially financed with contributions from the partners and, per the terms of the joint venture agreement, the partners may be required to provide additional capital contributions in the future.

11. Variable Interest Entities

From time to time the Company may form joint ventures with third parties for the execution of single contracts or projects. In accordance with ASC 810, the Company assesses its joint ventures at inception to determine if any meet the qualifications of a VIE. The Company considers a joint venture a VIE if either (a) the total equity investment is not sufficient to permit the entity to finance its activities without additional subordinated financial support, (b) characteristics of a controlling financial interest are missing (either the ability to make decisions through voting or other rights, the obligation to absorb the expected losses of the entity or the right to receive the expected residual returns of the entity), or (c) the voting rights of the equity holders are not proportional to their obligations to absorb the expected losses of the entity and/or their rights to receive the expected residual returns of the entity, and substantially all of the entity’s activities either involve or are conducted on behalf of an investor that has disproportionately few voting rights. Upon the occurrence of certain events outlined in ASC 810, the company reassesses its initial determination of whether the joint venture is a VIE.

ASC 810 also requires the Company to determine whether it is the primary beneficiary of the VIE. The Company concludes that it is the primary beneficiary and consolidates the VIE if the Company has both (a) the power to direct the economically significant activities of the VIE and (b) the obligation to absorb losses of, or the right to receive benefits from, the VIE that could potentially be significant to the VIE. The Company considers the contractual agreements that define the ownership structure, distribution of profits and losses, risks, responsibilities, indebtedness, voting rights and board representation of the respective parties in determining if the Company is the primary beneficiary. The Company also considers all parties that have direct or implicit variable interests when determining whether it is the primary beneficiary. In accordance with ASC 810, management’s assessment of whether the Company is the primary beneficiary of a VIE is performed continuously.

As of December 31, 2017, the Company’s Consolidated Balance Sheet included current and noncurrent assets of $95.5 million and $11.6 million, respectively, as well as current liabilities of $140.7 million related to the operations of its consolidated VIEs.

One large joint venture that the Company is consolidating was established to construct the Purple Line Segment 2 Extension project, a $1.4 billion mass-transit project in Los Angeles, California. The Company has a 75% interest in the joint venture with the remaining 25% held by O&G Industries, Inc. The joint venture was initially financed with contributions from the partners and, per the terms of the joint venture agreement, the partners may be required to provide additional capital contributions in the future.